1. Field of the Invention
The present invention relates to an apparatus and method for providing an output signal indicative of engine rotational speed and/or generator rotational speed. The present invention also relates to a voltage regulator adapted to determine engine rotational speed and/or generator rotational speed based on a ripple on a positive voltage input to the voltage regulator from a generator, and a charging system containing such a voltage regulator.
2. Discussion of the Related Art
Voltage regulating systems for controlling the field current of a diode-rectified alternating current generator, that supplies the electrical loads on a motor vehicle, are well known to those skilled in the art. One known type of voltage regulator senses the voltage applied to the battery, and if this voltage is higher than a desired regulated value, a transistor that controls field current is switched off. When generator voltage drops below the regulated value, the field controlling transistor is switched on. The transistor is repetitively switched on and off in response to sensed voltage changes to thereby cause the output voltage of the generator to be maintained at a predetermined, desired regulated value.
In another type of known voltage regulator the field current is pulse-width modulated at a constant frequency to maintain the output voltage of the generator at a desired regulated value. The pulse width, in that type of system, is a function of the difference between actual generator output voltage and a desired voltage. Examples of this type of regulator are disclosed in U.S. Pat. No. 2,976,473 to Shaw et al. and U.S. Pat. No. 4,275,344 to Mori et al. British Pat. No. 1,392,096 also discloses pulse-width control of field current, and in that patent, the voltage reference takes the form of a cyclic staircase waveform.
Another example of a voltage regulator that employs pulse width modulation of generator field current is disclosed in U.S. Pat. No. 4,636,706 to Bowman et al., the contents of which are incorporated herein by reference. According to Bowman et al., the regulator disclosed in that patent utilizes a digital apparatus that includes an up-down counter which responds to the relative magnitudes of the actual output voltage of the generator and the desired regulated output voltage of the generator. When the actual output voltage of the generator is below the desired regulated value, the counter is incremented or counted up, and when the actual output voltage is above the desired regulated value, the counter is decremented or counted down. The instantaneous count in the counter is used to determine the on time of a semiconductor switch that is connected in series with the field winding of the generator. The instantaneous count thus determines the pulse-width of the voltage that is applied to the field. Whenever actual output voltage exceeds the desired regulated value, the field controlling semiconductor switch is biased off. Thus, during the time that the actual output voltage is above the desired regulated value, the field is not energized and the counter is decremented. When actual output voltage then drops below the desired regulated value, the field is energized at the pulse-width represented by the magnitude of the count in the counter, and the counter is incremented.
A particularly advantageous feature of the Bowman et al. voltage regulator is its ability to adjust the counting rate of the counter based on engine speed. By suitably adjusting the counting rate, the voltage regulator is able to minimize the increased torque load that is applied to the engine by the generator when a large electrical load is applied to the generator at the time that the engine and generator are operating at a low speed such as engine idle speed. Thus, during engine idle, field current is gradually increased so as not to impose a sudden torque load on the engine when a large electrical load is applied to the generator. Since this type of voltage regulator is responsive to engine rotational speed and/or generator rotational speed, it requires an input signal indicative of that speed.
According to the Bowman et al. patent, this input signal is provided by tapping one of the stator winding phases. This phase of the stator winding is tapped by electrically connecting the appropriate input terminal of the voltage regulator to an AC node 32 of the bridge rectifier that is connected to that phase. FIG. 1 shows a broken line 7 from node 32 to the voltage regulator as an example of such an electrical connection.
While the resulting arrangement is generally effective, the additional electrical connection 7 from node 32 to the voltage regulator remains susceptible to damage, breakage, disconnection, deterioration by environmental contamination and/or exposure, and the like. The susceptibility of the resulting arrangement, in turn, can result in repair and/or warranty costs. It also makes installation more complicated, inasmuch as a dedicated electrical connection must be run from that node 32 to the voltage regulator. Typically, the connection at node 32 is made using soldering/welding techniques. Such connections, however, can prove unreliable over time and over many operations of the engine. While these problems can be avoided by using a minimum function type of voltage regulator that does not respond to engine and/or generator speed, this comes at the expense of foregoing the advantages of engine/generator speed-responsive operation of the voltage regulator.
There is consequently a need in the art for a way of providing a signal indicative of engine and/or generator speed without having to make an electrical connection from the junction 32 to the voltage regulator. Since it is desirable to minimize the number of wires that are connected to the voltage regulator of an engine, this need extends to providing this engine/generator speed-indicative signal without requiring any input electrical connections at the voltage regulator other than the positive voltage output from the bridge rectifier and electrical ground.